Apparatus and method for subgrade preparation

ABSTRACT

A subgrade preparation apparatus is operable to level, accurately grade and compact a subgrade surface for receiving a preformed concrete slab on the subgrade, in order to repair a concrete surface. The subgrade preparation apparatus includes a base unit, an extendable boom extending from the base unit, and a screed head assembly vertically adjustable on the extendable boom. The base unit is positionable on the concrete surface being repaired. The screed head assembly is vertically adjustable to be lowered into a cut out area defining the subgrade. Preferably, the screed head assembly includes a plow, auger and/or vibrator for grading, leveling and/or compacting the subgrade surface, and is further operable to grade, level, compact and/or smooth the subgrade surface close to the edges or walls of the cut out area.

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority on U.S. provisional application, Ser. No. 60/359,916, filed Feb. 27, 2002 by Quenzi for APPARATUS FOR SUBGRADE PREPARATION, which is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] The present invention relates generally to screeding devices and, more particularly, to a screeding device which is adapted for use in grading and smoothing a subgrade for placing a prefabricated or preformed concrete slab thereon.

BACKGROUND OF THE INVENTION

[0003] Typically, repair of concrete surfaces, such as roads, highways, airport runways or the like, requires closing of the particular surface being repaired for an extended period of time. This is because repairs have conventionally been performed by cutting out the damaged area and patching the cut out area with asphalt or poured or placed uncured concrete. The patched area then cannot be driven on until the asphalt or uncured concrete has time to cure and harden. This may take several hours or days, depending on the material used, the weather conditions and the size of the patched area.

[0004] Recently, a new process has been developed whereby a section of the damaged surface is cut out and replaced with a preformed concrete slab. An example of this process is disclosed in U.S. patent application Publication No. U.S. 2001/0018006, published Aug. 30, 2001, which is hereby incorporated herein by reference. The proposed process requires substantially less time to complete the repair of the concrete surface, since the preformed concrete slab does not require additional time to cure. However, in order to avoid cracking or breaking of the preformed concrete slab, the subgrade or subsurface, which is typically formed from dirt, sand, gravel, stone dust, or combinations thereof, must be leveled and smoothed prior to the slab being placed in the cut out repair area. The preparation of the subgrade surface is manual-labor intensive in order to provide a highly smooth and accurately contoured support surface for placing the preformed slab thereon. In addition, any undesired settling of the preformed slab or poor alignment with any of the surrounding slabs or features must be avoided through accurate placement and compaction of the subgrade materials. Accurate placement and compaction of the sub-grade materials is known to be highly difficult even with the aid of skilled personnel using special measuring tools and equipment. This adds to the cost and time required for the process of replacing the cutout section of concrete with the preformed or pre-cast concrete slab.

[0005] Therefore, there is a need in the art for an improved apparatus or device for providing an accurate, smooth and/or compacted subgrade surface for accurate placement and support of a preformed concrete slab onto the subgrade.

SUMMARY OF THE INVENTION

[0006] The present invention provides an apparatus for screeding, compacting, accurate grading, and vibrating a subgrade or subsurface for placing a preformed concrete slab onto the subgrade. The screeding apparatus of the present invention is operable to reach down and into the subgrade repair area from a level above the subgrade (the level above the subgrade corresponds generally with the existing concrete surface under repair), and to smooth and compact the subgrade to a desired grade so the preformed concrete slab will be uniformly supported on the subgrade once placed thereon.

[0007] According to an aspect of the present invention, a subgrade preparation apparatus is operable to level, grade and compact a subgrade surface for receiving a preformed concrete slab on the subgrade, in order to repair a concrete surface. The subgrade preparation apparatus includes a base unit, an extendable boom extending from the base unit, and a screed head assembly vertically adjustable on the extendable boom. The base unit is positionable on the concrete surface being repaired. The screed head assembly is vertically adjustable to be lowered into a cut out area of the concrete surface defining the subgrade. The screed head assembly includes a framework, a plow, and at least one of a means for moving material toward at least one side of the screed head assembly and a vibrator mounted to the framework for grading, leveling and/or compacting the subgrade surface. The plow has at least one outer end which defines an outermost portion of the screed head assembly such that the screed head assembly is operable to grade, level, compact and/or smooth the subgrade surface close to the walls of the cut out area.

[0008] The plow of the screed head assembly may include a main plow and one or more plow wings which extend laterally outward from the main plow for plowing the subgrade surface along the edges or walls of the cut out area. The outer end of the plow wing defines the outer end of the plow as an effective material engagement element.

[0009] The means for moving material toward at least one side of the screed head assembly may include an auger or other device for engaging the subgrade and moving material to a side of the screed head assembly, such as a continuous chain or belt with paddles or other members for engaging the subgrade and moving therealong. The auger or other means for moving material includes an inboard mounted motor to further facilitate moving the screed head assembly to close proximity of the edge of an adjacent concrete slab, wall, or feature of the cut out area without contact interference by the motor, its support brackets, or hydraulic line connections.

[0010] The present invention further provides for enhanced ease of cleaning and/or maintenance of the screed head components. The plow may be pivotally mounted to a framework of the screed head assembly to allow for pivotal movement of the plow for access to the plow and/or auger and/or other components of the screed head assembly. Likewise, the auger or other means for cutting and/or moving material may be pivotally mounted to the framework to vertically adjust the auger relative to the framework and to allow the auger to be pivoted away from the framework in order to access and clean and/or repair the auger and/or other components of the screed head assembly.

[0011] The subgrade preparation apparatus of the present invention includes an elevation device which is operable to lower and raise the screed head assembly relative to the boom and the base unit. The elevation device is operable to lower the screed head assembly a substantial amount to allow the screed head assembly to reach the subgrade below the concrete surface and within the cut out area being prepared. The elevation device further includes a tilt limiting device which is operable to limit or substantially preclude excessive vertical movement of one side of the screed head assembly relative to the other side. Preferably, the elevation device is operable in response to a three dimensional profiler system commercially available from Somero Enterprises, such as disclosed in U.S. Pat. No. 6,227,761, issued May 8, 2001 to Kieranen et al. and entitled APPARATUS AND METHOD FOR THREE DIMENSIONAL CONTOURING, which is hereby incorporated herein by reference, including at least one 3-D laser tracking target mounted to a portion of the elevation device. Additionally, the elevation device is operable in response to a laser reference plane established at the work site and at least one laser receiver mounted to a portion of the elevation device.

[0012] The elevation device may be a pair of electromechanical linear actuators, or preferably, hydraulic cylinders having a cylinder and a piston rod extendable and retractable relative to the cylinder. The cylinders may be mounted to the extendable boom, while the screed head assembly is mounted to the lower ends of the piston rods. Accordingly, no additional screed head elevation devices, structural tubes, or mechanical elements are required to mount and adjust the screed head to the extendable boom. This provides for an elevation device which has a substantially greater available range of motion or stroke travel over conventional elevation devices for screeding devices for uncured concrete. This feature provides the machine the ability to lower the screed head assembly of the present invention a sufficient amount below the concrete surface and within the cut out area under repair.

[0013] The screed head assembly is preferably of a relatively narrow width to facilitate access and maneuverability of the screed head assembly within various sized cut out areas of concrete to be repaired. Preferably, the screed head assembly is only approximately six to eight feet wide (approximately 1.82 to 2.43 meters), however other widths outside of this range are feasible as may be desired or required for the particular application of the subgrade preparation apparatus.

[0014] According to another aspect of the present invention, a method for leveling, accurate grading and/or compacting a subgrade surface for receiving a preformed concrete slab on the subgrade to repair a concrete surface above the subgrade surface includes providing a subgrade preparation apparatus having a base unit and a screed head assembly. The base unit is positionable on the concrete surface being repaired. The screed head assembly includes a plow which defines at least one end. The screed head assembly has no major projections extending laterally outwardly from the end of the plow. The method includes vertically moving the screed head assembly relative to the extendable boom into a cut out area of the concrete surface defining the subgrade, generally horizontally moving the screed head assembly along the subgrade surface, and accurately grading, leveling and/or compacting the subgrade surface close to the walls of the cut out area with at least one of the plow, a means for moving material to one side of the screed head assembly and a vibrator of the screed head assembly.

[0015] According to another aspect of the present invention, a subgrade preparation apparatus for leveling, accurate grading and/or compacting a subgrade surface for receiving a preformed concrete slab on the subgrade to repair a concrete surface above the subgrade surface includes a base unit, an extendable boom, a screed head assembly, a pair of spaced-apart actuators and a tilt limiting device. The base unit is positionable on the concrete surface being repaired. The extendable boom extends from the base unit and has the screed head assembly adjustably mounted on the extendable boom. The screed head assembly is vertically adjustable relative to the extendable boom so as to be lowerable into a cut out area of the concrete surface defining the subgrade surface below the concrete surface. The screed head assembly includes a framework and at least one of a plow, a means for moving material toward at least one side of the screed head assembly and a vibrator mounted to the framework for accurate grading, leveling and/or compacting the subgrade surface. The pair of actuators is mounted on the extendable boom and connected to the screed head assembly at spaced positions on the screed head assembly. The actuators are operable to extend and retract to vertically move the screed head assembly relative to the extendable boom and the base unit. The tilt limiting device is operable to detect a maximum permissible degree of tilt of the screed head assembly and to deactuate at least one of the pair of actuators in response to a threshold degree of tilt of the screed head assembly.

[0016] According to yet another aspect of the present invention, a subgrade preparation apparatus for leveling, accurately grading and compacting a subgrade surface for receiving a preformed concrete slab on the subgrade to repair a concrete surface above the subgrade surface includes a base unit, an extendable boom and a screed head assembly. The base unit is positionable on the concrete surface being repaired, while the extendable boom extends from the base unit. The screed head assembly is adjustably mounted on the extendable boom. The screed head assembly is vertically adjustable relative to the extendable boom and includes a framework, an auger device for moving material toward at least one side of the screed head assembly and at least one of a plow and a vibrator mounted to the framework for grading, leveling and/or compacting the subgrade surface. The auger device includes a rotatable portion rotatably mounted to and extending laterally across the framework and a drive motor for rotatably driving the rotatable portion. The drive motor is positioned at least partially laterally inboard of the outer end of the rotatable portion such that the screed head assembly is operable to grade, level, compact and/or smooth the subgrade surface close to at least one wall at least partially surrounding the subgrade surface.

[0017] Therefore, the subgrade preparation apparatus of the present invention is operable to accurately grade, level and/or compact a subgrade surface which may be positioned at a level substantially lower than a support surface for the apparatus. The screed head assembly is lowerable a significant amount to reach into a cut out area of the support surface to accurately grade, level and/or compact the subgrade surface. The screed head assembly is controlled to limit over extension or retraction of one side relative to the other as the screed head assembly is lowered into the cut out area. This aspect of the invention prevents the mechanical elements of the device from becoming potentially physically damaged due to operator error as a result of over-extension of the elevation actuators. The subgrade preparation apparatus is capable of accurately grading, leveling and/or compacting substantially the entire area of the subgrade surface within a cut out area, including the area immediately adjacent to the walls or limiting features of the cut out area, such that manual labor requirements are substantially reduced and a highly accurate and superior quality subgrade is produced, for the immediate placement and support of a pre-cast concrete repair slab within a roadway, parking area, airport runway, or the like.

[0018] These and other objects, advantages, purposes and features of this invention will become apparent upon review of the following specification in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a top perspective view of a subgrade preparation apparatus in accordance with the present invention;

[0020]FIG. 2 is a side elevation of the subgrade preparation apparatus of FIG. 1, positioned at a cut out area of a concrete surface being repaired;

[0021]FIG. 3 is a top plan view of the subgrade preparation apparatus of FIGS. 1 and 2;

[0022]FIG. 4 is an upper perspective view of a screed head assembly and elevation assembly in accordance with the present invention;

[0023]FIG. 5 is an exploded perspective view of the elevation assembly and mounting assembly of FIG. 4;

[0024]FIG. 6 is a side elevation of an elevation cylinder of the present invention;

[0025]FIG. 7 is a sectional side elevation of the elevation cylinder taken along the line VII-VII in FIG. 6;

[0026]FIG. 8 is a front elevation of the screed head assembly and elevation assembly of the present invention, showing a schematic of a tilt limiting device useful with the present invention;

[0027]FIG. 9 is an upper perspective view of the screed head assembly of FIG. 4, with the elevation assembly and mounting assembly removed;

[0028]FIG. 10 is an exploded perspective view of the screed head assembly of FIG. 9;

[0029]FIG. 11 is an enlarged exploded perspective view of the attachment of an elevation cylinder to a side of the screed head assembly;

[0030]FIG. 12 is a front elevation of a vibrator assembly of the screed head assembly of FIG. 4;

[0031]FIG. 13 is an upper perspective view of the screed head assembly of FIG. 4, with the vibrator assembly, elevation assembly and mounting assembly removed;

[0032]FIG. 14 is an end elevation of the screed head assembly of FIG. 4;

[0033]FIG. 15 is an opposite end elevation of the screed head assembly of FIG. 14;

[0034]FIG. 16 is a lower perspective view of the screed head assembly of FIG. 13, with the plow pivoted upward;

[0035]FIG. 17 is an end elevation of the screed head assembly of FIG. 16;

[0036]FIG. 18 is an opposite end elevation of the screed head assembly of FIG. 17 with the auger assembly pivoted downward;

[0037]FIG. 19 is an end elevation of the screed head assembly of FIG. 4, showing a height adjustment tool and procedure for the auger and the plow;

[0038]FIG. 19A is an enlarged perspective view of the area XIXA-XIXA in FIG. 19; and

[0039]FIG. 20 is an end elevation of the auger assembly of the present invention, showing a chain tension adjustment procedure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Referring now specifically to the drawings and the illustrative embodiments depicted therein, a subgrade preparation apparatus, machine or device 10 includes a wheeled base unit 12 and an extendable or telescoping boom assembly 14 which extends from base unit 12 (FIGS. 1-3). A screed head assembly 16 is adjustably mounted at an outer end 14 a of extendable boom 14 and is vertically adjustable relative to outer end 14 a via an elevation assembly 18. The wheeled base unit 12 is movable over an existing concrete surface 11 a, such as a section of highway pavement, airport runway, or the like, and is positionable adjacent to a section of the concrete which has been removed to expose a subgrade or sub-surface 11 b (FIG. 2). Since the concrete section has been removed, the exposed subgrade or subsurface is typically sand, mixed soil or dirt, gravel or the like. The screed head assembly 16 is extendable out over the subgrade via the extendable boom 14 (see FIGS. 2 and 3) and then lowered down to the subgrade surface 11 b via the elevation assembly 18.

[0041] Screed head assembly 16 includes a plow assembly 46 extending generally laterally along a framework 48 of screed head assembly 16, as discussed in detail below. Plow assembly 46 includes a main plowblade 46 a and opposite ends 46 d which define an outermost portion of the screed head assembly. In other words, the outer end or ends 46 d of the plow assembly 46 is/are positioned at or extend outwardly from an outermost portion of framework 48 and/or from an outermost portion of other components of screed head assembly 16, such as an auger 44 or a vibrator device 42 (discussed in detail below). Preferably, the plow assembly 46 is at least as long as or longer than the width of the framework 48, and at least as long as or longer than the auger 44 and vibrator device 42 of screed head assembly 16. Because there are no components extending laterally outwardly from screed head assembly 16 substantially beyond the outer end or ends of the plow assembly, the outer end or ends 46 d of the plow assembly 46 are able to engage the subgrade surface substantially immediately adjacent to the side walls of the cut out area to plow the subgrade surface as screed head assembly 16 is moved over and along the subgrade surface. As discussed below, the plow assembly 46 may include a plow wing or plow wings 54 positioned at the outer end or ends of the main plow blade 46 a, such that the outer ends 46 d′ of the plow wings 54 define the outermost portion of the screed head assembly and extend laterally outwardly beyond the outermost portions of the frame or other components of the screed head assembly 16.

[0042] Screed head assembly 16 further defines opposite side walls or surfaces 17, which are substantially flat, such that no major projections extend or protrude therefrom, as is best seen in FIGS. 1, 4, 9 and 19. By no major projections, it is meant that no components or major structural members, such as motors, mounting brackets and the like, extend laterally outward from the side walls 17 of the screed head assembly 16, except for minor parts, such as bolts or other fasteners or the like. Particularly, no drive motors or other components associated with the devices of the screed head assembly (discussed below) project outwardly from the side walls or surfaces of the screed head assembly. This allows the outer ends of the plow of the screed head assembly of the present invention to compact and smooth the subgrade to a desired grade up to and immediately adjacent to the side walls of the cut out area that is under repair. Such side walls are generally vertical with respect to the subgrade surface and the concrete surface since they typically are cut with a concrete saw supported on the concrete surface.

[0043] The screed head assembly 16 is then operable to compact, smooth, accurately grade and level the subgrade surface to a desired grade, such that the subgrade will uniformly support a preformed concrete slab placed thereon. This process results in a substantially compacted and smooth, even and level subgrade surface which substantially precludes cracking or breaking of the preformed slab placed thereon, which may result if it is unevenly supported by the subgrade. Preferably, the screed head assembly 16 is approximately six feet to eight feet (approximately 1.82 to 2.43 meters) wide so that the screed head assembly is maneuverable within a cut out area where concrete has been removed. The smaller size of the screed head assembly 16 allows for repair of a variety of sizes of damaged or cut out areas and allows for easier maneuverability of the screed head assembly within the cut out area.

[0044] Wheeled base unit 12 and boom assembly 14 of subgrade preparation apparatus 10 are substantially similar to the base unit and boom assembly disclosed in U.S. Pat. Nos. 4,930,935; 6,183,160; 6,152,647; and/or 6,129,481, which are hereby incorporated herein by reference, such that a detailed discussion of the base unit 12 and boom assembly 14 will not be included herein. Briefly, as shown in FIGS. 1-3, base unit 12 includes a lower support frame 20 having front and rear propulsion support axles 22, each of which may provide both propulsion and steering capability, four support wheels 26, preferably including rubber tires, and an upper frame 28, which is preferably rotatable on a bearing assembly (not shown) supported on lower frame 20 and includes an operator support platform 30 along with an engine/hydraulic pump compartment 32. The wheels 26 on axles 22 are preferably individually powered by hydraulic motors or other means for independently driving the wheels 26 of base unit 12.

[0045] The bearing assembly is substantially similar to that described in U.S. Pat. No. 4,655,633, the disclosure of which is hereby incorporated by reference herein, and is powered by an hydraulic rotation motor (not shown) which is operable to rotate the upper framework 28 with respect to the lower framework 20 through 360 degrees. Four extendable, telescoping stabilizer legs 34, one at each corner of support frame 20, and each including a ground engaging foot or plate 34 a, are extendable and retractable by separate hydraulic cylinders and may extend downwardly to engage the concrete surface or other support surface when the subgrade preparation apparatus 10 is positioned adjacent to a cut out area to be compacted and screeded for the pre-formed concrete slab, as can be seen in FIG. 2. Extension of the legs 34 may lift or support the entire apparatus off the wheels and tires 26 as needed to provide a stabilized support platform during extension and retraction of boom assembly 14 and screed head assembly 16 and during preparation of the subgrade. Alternately, extension of legs 34 to support the entire apparatus may not require fully lifting the wheels and tires off the support surface in that substantial support is also gained by having both the extension legs and tires remaining in firm contact with the surface. Upper frame 28 also provides support for the telescoping boom assembly 14.

[0046] Boom assembly 14 extends outwardly from upper frame portion 28 below the operator's platform 30 and is mounted for horizontal, telescoping extension and retraction on suitable bearings, as is described in U.S. Pat. No. 4,655,633, incorporated by reference above. On the outer, free end 14 a of boom assembly 14 is a mounting assembly 36 (FIGS. 1, 4 and 5) to which elevation assembly 18 is attached. Screed head assembly 16 is, in turn, mounted to the elevation assembly 18 and is vertically adjustable with respect to the subgrade and boom assembly 14 via elevation assembly 18. By means of the rotatable upper frame portion 28, boom assembly 14, carrying mounting assembly 36, elevation assembly 18 and screed head assembly 16, may be rotated 360 degrees around lower frame 20 of base unit 12 on the bearing assembly to swing or move the screed head assembly over a targeted area for compacting, smoothing and/or grading and leveling, i.e., screeding, the subgrade or surface of the targeted area 11 b adjacent to the base unit 12 of the subgrade preparation apparatus 10.

[0047] Preferably, the elevation device is operable in response to an automatic three dimensional profiler system commercially available from Somero Enterprises, such as disclosed in U.S. Pat. No. 6,227,761, issued May 8, 2001 to Kieranen et al. and entitled APPARATUS AND METHOD FOR THREE DIMENSIONAL CONTOURING, which is hereby incorporated herein by reference, including at least one 3-D laser tracking target mounted to a portion of the elevation device (not shown).

[0048] Optionally, an automatic elevation control system, preferably using laser beacon receivers 38 (FIG. 1) and a laser reference plane generator (not shown), is included on elevation assembly 18 and is connected to an appropriate control (also not shown), which may be mounted on operator platform 30 on upper frame portion 28.

[0049] As described in U.S. Pat. No. 4,655,633, incorporated by reference above, mounted within engine compartment 32 is a conventional internal combustion diesel, gasoline, or electric engine, or other power source (not shown). Preferably, the engine provides power to a single, variable displacement, hydraulic pump (also not shown), which is preferably load-sensing and draws and returns hydraulic fluid from a tank or reservoir (also not shown) that is also mounted on upper frame 28. The engine compartment 32 also houses a battery for starting the engine and providing power to the various electrical controls and various hydraulic system components.

[0050] As shown in FIGS. 4 and 5, mounting assembly 36 includes a cross member 36 a, which includes a pair of mounting brackets 36 b spaced from each other along cross member 36 a. Each of the pairs of mounting brackets 36 b includes a mounting bracket at both the forward and rearward sides or faces of the cross member 36 a. The mounting attachment or brackets 36 b are adapted to receive or connect to a mounting bracket 14 b extending downward from outer end 14 a of boom assembly 14, as shown in FIG. 1. An elongated pin, bolt or fastener 35 (FIG. 4) is provided which extends generally through the center of cross member 36 a and mounting bracket 14 b of boom assembly 14 to allow for pivotal movement of the head assembly 16 relative to boom 14 when the brackets 36 b are disconnected from boom 14.

[0051] Mounting assembly 36 further includes trunnion mounting plates 36 e each having bearings 36 f which support a lower end portion 19 c of elevation actuator 19 and provide a pivot axis 36 g as shown in FIG. 5. Pivot motion of one cylinder 19 a may be fixed at one side of mounting assembly 36 by upper and lower partially circular stop plates 36 d having radius collar 36 c. Partially circular stop plates 36 d are bolted into place (bolts not shown) and generally vertically spaced apart by cross member 36 a and therefore limit the motion of elevation cylinder 19 to a fixed vertical position. Free pivot motion of opposite elevation cylinder 19 about axis 36 g is provided by bearings 36 f and trunnion mounting plates 36 e. The degree of freedom of movement thus provided of screed head assembly 16 is best shown in FIG. 8, with one elevation cylinder in a fixed vertical position and the opposite elevation cylinder able to pivot about axis 36 f as needed to accommodate the controlled motion of screed head assembly 16 and elevation assembly 18 during operation.

[0052] As also shown in FIGS. 4 and 5, elevation assembly 18 comprises a pair of elevation actuators 19, which are preferably hydraulic cylinders, whereby each includes an outer cylinder 19 a and a piston rod 19 b movable along and within cylinder 19 a. Lower end or portion 19 c of each cylinder 19 a is mounted to a respective collar 36 c of mounting assembly 36 via mounting plates 36 e and bearings 36 f such that the cylinders 19 a may be generally fixedly or pivotally secured to mounting assembly 36. A lower end 19 d of each piston rod 19 b is secured to a mounting bracket 37 secured to or toward a respective side of the screed head assembly 16, as best shown in FIG. 11 and as discussed below.

[0053] The laser receivers 38 are mounted above or near the opposite or upper ends 19 e of piston rods 19 b. In the illustrated embodiment, laser receivers 38 are mounted to upper ends 39 a of rods 39 which are insertable within piston rods 19 b and secured relative thereto via a pair of clamps 39 b, as can be seen with reference to FIGS. 1 and 5. The rods 39 are vertically adjustable along and within piston rods 19 b to set the laser receivers 38 at an appropriate height above the upper ends 19 e of piston rods 19 b. Because the rods 39 are secured to the piston rods 19 b, the laser receivers 38 are vertically movable with the piston rods 19 b, such that the vertical position of the piston rods 19 b relative to the cylinders 19 a and, thus, relative to boom assembly 14 and base unit 12, is adjustable in response to and for positioning with respect to the laser receivers 38 and the laser reference plane.

[0054] Optionally the laser receivers 38 may be replaced with at least one three dimensional tracking target (not shown) and one sonic height sensor (not shown) for use with an automatic three dimensional profiler system commercially available from Somero Enterprises, such as disclosed in U.S. Pat. No. 6,227,761, issued May 8, 2001 to Kieranen et al. and entitled APPARATUS AND METHOD FOR THREE DIMENSIONAL CONTOURING, which is hereby incorporated herein by reference.

[0055] As shown in FIGS. 6 and 7, elevation cylinder 19 is a double-ended hydraulic cylinder, such that piston rod 19 b is extendable in either direction relative to cylinder 19 a. Piston rod 19 b is substantially longer than cylinder 19 a, such that lower end 19 d of piston rod 19 b may extend from the lower end of cylinder 19 a, while upper end 19 e of piston rod protrudes from the upper end of cylinder 19 a. Piston rod 19 b includes a piston seal member 19 f which is positioned generally around a middle portion of piston rod 19 b. The length of piston rod 19 b allows for significant extension and retraction of lower end 19 d of piston rod 19 b relative to cylinder 19 a, which results in significant lowering and raising of screed head assembly 16 relative to boom assembly 14 and base unit 12, in response to pressurized hydraulic fluid within cylinder 19 a at either side of piston seal member 19 f. Additionally, with the double-ended hydraulic cylinder 19, a characteristic of generally equal response or displacement of the cylinder in either the raising or lowering direction is provided for a given volume of pressurized hydraulic fluid, which results in generally equal system response in both directions. This enhances the control of the grade or level of the screed head assembly in response to the laser leveling or three dimensional automatic control systems.

[0056] Because the elevation cylinders are incorporated into the screed head elevation tubes, and are not separate actuators (as is the case with known screeding devices for uncured concrete applications), the elevation cylinders of the present invention are capable of an increased stroke to allow the screed head assembly 16 to be lowered substantially downward and into the cut out work area or area under repair to reach the subgrade. In the illustrated embodiment, elevation assembly 18 is operable to lower screed head assembly 16 downward approximately eighteen inches (approximately 45.7 cm) below the level of the existing concrete which supports the base unit 12. Therefore, the elevation assembly of the present invention may lower the screed head assembly to a subgrade well below the concrete surface of the road or slab that is being repaired. The depth of the subgrade is adjusted to correspond with the thickness of the preformed concrete slab to be placed thereon.

[0057] Each of the elevation cylinders 19 are operable independently from one another, such as in response to the laser receivers 38. Because of the increased degree of extension and retraction of the respective elevation cylinders, and the relatively short distance between them at the respective axis 36 g at mounting assembly 36 (which effectively serves as a generally fixed mechanical link), the elevation assembly may bind if one elevation cylinder 19 is extended or retracted significantly more than the other. This may then result in damage to the mounting assembly 36 and/or the screed head assembly 16. In order to limit or preclude binding and/or mechanical damage of the elevation assembly, subgrade preparation apparatus 10 preferably further includes a tilt limiting device 40 (FIG. 8), which is operable to limit vertical movement of one side of screed head assembly 16 relative to the other, such as via limiting extension or retraction of one extension actuator or cylinder relative to the other, in order to prevent excessive tilt or twist of the screed head assembly 16, which may further cause binding of the elevation cylinders.

[0058] In the illustrated embodiment of FIG. 8, tilt limiting device 40 includes a tilt switch box or limit switch 40 a on screed head assembly 16 which measures or detects the degree of tilt of screed head assembly 16. The elevation cylinders 19 further include raise tilt pilot valves 40 b and lower tilt pilot valves 40 c for controlling the hydraulic fluid at the lower and upper ends of the cylinders, respectively, in response to corresponding elevation valves 40 d. The tilt switch box 40 a may comprise any means for determining a degree of offset from level of the screed head assembly and for generating a signal (such as an electrical signal or mechanical switch) when the degree of offset or tilt reaches a predetermined, threshold amount. Accordingly, as the slope or tilt limit or threshold of the screed head assembly is reached, the tilt switch box 40 a sends a signal to close the appropriate tilt pilot valves (for example, the raise tilt pilot valve 40 b of one elevation cylinder and/or the lower tilt pilot valve 40 c of the other elevation cylinder) to prevent further extension or retraction of one or both of the elevation cylinders 19. Tilt limiting device 40 thus limits one side of the screed head assembly 16 from being lowered or raised a predetermined amount (for example, approximately 10 inches) more than the other side of the screed head assembly, in order to prevent damage to the subgrade preparation apparatus 10.

[0059] Referring now to FIGS. 1 and 9-18, screed head assembly 16 includes a vibrator assembly 42, an auger assembly 44 and a plow assembly 46 mounted to a framework 48. As best shown in FIGS. 10, 13, 14 and 16-18, framework 48 includes a pair of side brackets 48 a and cross members 48 b and 48 c. Vibrator assembly 42 is mounted to and between a rearward end of side brackets 48 a, while plow assembly 46 is adjustably mounted to the opposite or forward end of side brackets 48 a, generally along cross member 48 b. Auger assembly 44 is mounted at opposite ends to brackets 48 a and extends across framework 48 between vibrator assembly 42 and plow assembly 46.

[0060] As best shown in FIGS. 10 and 12, vibrator assembly 42 includes a pair of mounting tubes 42 a and a motor 42 b. Motor 42 b is operable to cause vibration of vibrator assembly 42 by rotating a shaft 42 f which includes a plurality of eccentric weights 42 c positioned therealong. Rotational driving of the shaft 42 f by the motor 42 b results in vibration of a lower contact plate 42 d along a lower edge of vibrator assembly 42. The contact plate 42 d engages the subgrade and vibrates to assist in compacting and smoothing the subgrade as the screed head assembly is moved along the subgrade by the boom assembly 14.

[0061] Each of the ends of the mounting tubes 42 a is mounted to a vibration isolator 42 e, which then mounts to a corresponding slot 43 in the side brackets 48 a of framework 48, as can be seen in FIGS. 9, 14, 15 and 19. The vibration isolators 42 e are preferably made of a substantially elastic or rubber material to absorb the vibration of the vibrator assembly and limit transmission of the vibration to the framework 48 of the screed head assembly 16. As shown in FIG. 14, the angle of the vibrator assembly 42 relative to the framework 48 may be adjusted by securing a threaded nut on a threaded stud 42 g extending from the vibration isolators 42 e at various locations along the upper mounting slots 43 (slot B in FIG. 14) in side brackets 48 a of framework 48. A measurable dimension C (FIG. 14) can be used as a reference for repeating desired or respective settings for the vibrator, when the lower isolators are positioned all the way forward (or otherwise at a known or repeatable location) in the lower mounting slots (slot A in FIG. 14). As shown in FIG. 14, the angle of vibrator 42 may be adjusted such that a trailing edge 42 h of contact plate 42 d contacts the ground or subgrade surface at a desired angle. The angle of the contact plate 42 d may then be set by measuring the dimension F of the leading edge 42 i of the contact plate above a level surface 51 when the trailing edge 42 h contacts the level surface. The dimension F may vary depending on the application of the subgrade preparation device.

[0062] Auger assembly 44 is operable to engage the subgrade surface and cut or establish the level or grade of the subgrade as the screed head assembly 16 is moved along and over the subgrade. In the illustrated embodiment, auger assembly 44 includes an auger 45, which includes a cylindrical portion 45 a and a spiraling or helical blade or flighting 45 b along the cylindrical portion 45 a (FIG. 10). However, the screed head assembly of the present invention may otherwise include other means for engaging the subgrade surface and cutting and/or moving excess material toward either side of the screed head assembly, without affecting the scope of the present invention. For example, the screed head assembly may include a continuous belt or chain which is movable and which has one or more paddles or extensions extending therefrom for engaging the subgrade surface and moving material toward one side of the screed head assembly, without affecting the scope of the present invention.

[0063] As best shown in FIG. 10, each of the opposite ends of auger 45 are rotatably mounted to an auger swing arm 50, which is pivotally mounted to side brackets 48 a at or near the plow end of the framework 48, such as at a bolt or pin 50 a. A second attachment pin or fastener 50 b is secured to each swing arm 50 and side bracket 48 a to secure the swing arm 50 at a desired orientation relative to the side bracket and thus preclude pivotal movement of the swing arm. As shown in FIGS. 14-19, swing arm 50 is movable relative to the second attachment fastener 50 b along a slot 50 c, to allow for adjustment of the swing arm 50, and thus of the height of the auger 45, relative to the framework 48. Each of the swing arms 50 may be adjusted by loosening the second fastener 50 b and loosening a third locking fastener or adjustment stop 50 d, and then prying or raising the swing arm 50 upward or downward, such as with a pry bar 53 having its tip 53 a engaged with a respective tooth or notch 50 f and with the pry bar fulcrum 53 b at a fixed bushing 50 g, to move both fasteners 50 b, 50 d along their respective slots (FIG. 19). Once the auger 45 is in the desired position, both fasteners 50 b, 50 d may be tightened to secure swing arm 50, and thus auger 45, relative to the framework 48.

[0064] Also, as shown in FIG. 18, second attachment fastener 50 b may be removed to allow swing arm 50 to swing or pivot about first attachment fastener 50 a to swing or move auger 45 downward and away from side brackets 48 a, in order to facilitate cleaning or maintenance of auger 45 and/or other components of screed head assembly 16 before or after use. Fastener 50 d may function to secure an adjustment stop 50 e in place on framework 48, such that the adjustment stop 50 e may remain secured during cleaning or maintenance operations and serve as a repeatable stop to preserve the desired adjusted height setting of the auger 45. As shown generally at dimension D in FIG. 14, swing arms 50 may pivot to adjust the height or position of auger 45, such that a lowermost contact portion or edge of flighting 45 b is substantially even or level with the trailing edge 42 h or contact point of contact plate 42 d of vibrator 42. The dimension D may vary depending on the application of the subgrade preparation device.

[0065] Auger 45 is rotated by a rotational drive motor 52 (FIGS. 10 and 16), which is mounted to swing arm 50 and on an inboard side of swing arm 50 and generally adjacent to or near one of the ends of auger 45. Motor 52 includes a sprocket or gear member 52 a, while an end or shaft 45 d of auger 45 likewise includes a sprocket or gear member 45 c, both of which extend to the outboard side of swing arm 50, but do not project substantially outwardly therefrom. A drive chain 52 b is routed around the sprockets 52 a and 45 c and drives the auger 45 in response to rotational driving from motor 52. A guard housing or cover plate 51 is mounted to swing arm 50 and encases chain 52 b and sprockets 52 a and 45 c to act as a safety shield and reduce the likelihood of contaminants, such as dirt, dust and the like, from reaching the moving and driving components of the auger assembly 44. By positioning the auger drive motor 52 inboard of the side edge of the screed head assembly 16, the present invention allows the vibrator, auger and plow of the screed head assembly to be moved relatively close to the edge wall of the cut out area being prepared by subgrade preparation apparatus 10.

[0066] As shown in FIG. 20, the position or separation of the sprockets 52 a, 45 c may be adjusted by loosening the respective bearing bolts to move the auger motor 52 and/or auger shaft 45 d relative to the swing plate 50, in order to tighten the chain 52 b around the sprockets 52 a, 45 c. The motor and auger shaft may be movably mounted within oversized holes 50 h (FIG. 10) in swing arms 50 to allow for such adjustment. The auger motor bolts and bearing bolts may then be tightened to secure the auger motor and auger shaft in a desired location relative to one another such that an appropriate amount of tension is in drive chain 52 b.

[0067] As best shown in FIGS. 10 and 13-19, plow assembly 46 includes a plow blade 46 a for engaging and moving or knocking down any excess dirt or the like at the subgrade. Plow assembly 46 is pivotally mounted to forward cross member 48 b of framework 48 at a pair of spaced mounting brackets 48 d extending upward from an upper surface of cross member 48 b. Each mounting bracket 48 d includes a pair of spaced apart plates which receive a mounting extension 46 b of plow assembly 46 therebetween. The mounting extensions 46 b are secured to the mounting brackets 48 d by a respective pin or bolt 46 c. Preferably, the spaced apart plates include generally vertical slots 48 e, such that the mounting extensions 46 b of plow assembly 46 are vertically adjustable relative to mounting brackets 48 d to allow for vertical adjustment of plow assembly 46 relative to framework 48. As shown in FIGS. 14, 15, 19 and 19A, one or more shims 47 may be positioned beneath mounting extensions 46 b to prevent lowering of the mounting extensions, and thus of the plow blade 46 a, relative to the framework 48. The shims 47 may be inserted into slots 48 e in brackets 48 d and retained in position by a retainer pin 47 a (FIGS. 19 and 19A). More or less shims 47 may be added or removed to adjustably mount or position plow assembly 46 at a desired height (dimension E in FIG. 4) relative to auger 44 and vibrator 42, such as approximately ½ inch (approximately 12.7 mm) above a generally level plane or surface 51 contacted by the contact surfaces of the auger and vibrator. The dimension E may vary depending on the application of the subgrade preparation device.

[0068] In the illustrated embodiment, plow assembly 46 is generally secured in a lowered, subgrade engaging position relative to the framework 48 by an adjustable biasing member or link 49 (FIG. 10), which pulls a lower portion of plow assembly 46 down and toward a lower portion of cross member 48 b. When the adjustable biasing member or link 49 is removed, plow assembly 46 may be pivoted about bolt 46 c at mounting brackets 48 d to allow for access to auger 45 and/or for cleaning or maintenance of plow assembly 46, as shown in FIGS. 16-18. Alternately, a mechanical stop or fastener or fasteners may be implemented to secure plow assembly 46 in the desired orientation relative to framework 48.

[0069] As shown in FIGS. 1, 4 and 9, the outer ends 46 d of plow assembly 46 define an outermost portion of the screed head assembly and, thus, extend outwardly from the outermost portions of the framework 48 and other components of the screed head assembly 16. Plow assembly 46 may further include an adjustable plow wing 54 at one or both ends of the main plow blade 46 a, whereby the outer ends 46 d′ of the plow wings 54 are positioned at or extend laterally outwardly from the framework and other components of the screed head assembly. Plow wing 54 extends laterally from the screed head assembly 16 to plow the area adjacent to the screed head assembly. In the illustrated embodiment, each plow wing 54 is pivotally mounted at a respective pivot pin 54 a at the opposite ends of the plow blade 46 a. An adjustable arm or bracket 55 extends between each wing 54 and a respective bracket 55 a along the upper portion of the plow. The adjustable bracket 55 is adjustable to set a degree of extension of the respective wing 54 to achieve an appropriate amount of extension of each wing for plowing dirt and the like as close to the edges or walls of the cut out area as possible. The plow wings thus may further minimize the amount of manual labor required to clean the edges of the subgrade before the preformed concrete slab is placed thereon. The plow wings 54 may further include a visual indicator 56 extending upward therefrom to provide visual indication to the operator of the subgrade preparation apparatus as to the position of the plow wings within the cut out area.

[0070] As shown in FIGS. 4 and 9, screed head assembly 16 may further include a tracing device 58, which is operable to generate a beam, such as a sonic tracing beam, downward along a side of the screed head assembly. Optionally, the tracing device 58 may detect the elevation of the finished surface of any previously screeded or accurately graded material such that a signal is sent to the elevation control system to establish matching of the current pass with any previously screeded material. Additionally, the tracing device 58 may alternately be set to detect edge features or side walls of the cut out area (in other words, the existing concrete adjacent to the cut out area), so the operator of subgrade preparation apparatus 10 can be made aware of the location of the screed head assembly 16 relative to the edge of the subgrade surface being prepared. This allows the operator to move the screed head assembly as close to the edge of the work area as possible to minimize the manual labor to clean up the edges of the subgrade.

[0071] As also shown in FIGS. 4 and 9, screed head assembly 16 may further include a second plow 60 mounted on the back or rearward side of vibrator assembly 42. The second plow 60 may then function as a rough grading device to initially knock down any excess compact dirt, sand or the like as screed head assembly 16 is moved in a the direction opposite to the normal direction of operation wherein plow 46 typically encounters material first.

[0072] During operation, base unit 12 may be driven on the existing concrete surface up to and substantially adjacent to the cut out area, as shown in FIG. 2. The stabilizers 34 may be lowered to engage the existing concrete surface to stabilize subgrade preparation apparatus 10 during processing of the subgrade surface. Extendable boom 14 is then operable to extend outward from base unit 12 to move screed head assembly 16 a desired amount out over the cut out area. For the first pass of the screed head assembly, the base unit 12 may be positioned such that the extendable boom positions the screed head assembly and/or the plow wing immediately adjacent to one wall or edge of the cut out area. When the screed head assembly 16 is positioned over the desired starting area, the elevation actuators 19 are actuated to lower the screed head assembly down toward and into engagement with the subgrade surface of the cut out area.

[0073] Once engaged with the subgrade surface, screed head assembly 16 is operable to smooth, compact, accurately grade and level the subgrade surface to the desired grade. The elevation actuators may be extended or pressurized or the like to apply a desired amount of down pressure to the subgrade surface with the screed head assembly. The extendable boom 14 retracts (or extends) to move the screed head assembly 16 over the subgrade surface as the plow, auger and vibrator engage and cut or smooth the surface. The plow 46 is preferably positioned at a forward side of the screed head assembly 16 and functions to initially engage and move or knock down any excess dirt or the like at the subgrade surface as the screed head assembly 16 is moved along and over the subgrade surface. The auger 44 or other material moving device is activated to engage and cut the subgrade surface and to move any excess material toward one side of the screed head assembly 16 and otherwise fill in any low areas with excess material, while the vibrator 42 may be vibrated as it engages the subgrade surface to smooth and compact the cut and cleared surface. As the screed head assembly is moved along the subgrade surface, the elevation actuators 19 are automatically operable by the control system to maintain the screed head assembly at a desired grade in response to the laser leveling or three dimensional control system, such that the subgrade surface is compacted and smoothed to the desired grade over substantially the entire subgrade surface of the cut out area.

[0074] After the extendable boom has moved the screed head assembly along the length of the cut out area, the screed head assembly may be raised above the subgrade surface and the movable unit may be pivoted or moved to align the extendable boom for a second pass over an adjacent portion of the subgrade surface which is adjacent to, and preferably partially overlapping, the first compacted and smoothed area. This is where the tracing device may be optionally utilized to detect the elevation of the previously finished surface and provide ideally matching surface elevations between successive passes. The process is then repeated until substantially the entire subgrade surface of the cut out area is compacted and smoothed to the desired grade. During the final pass along a wall or edge of the cut out area, the screed head assembly may be positioned substantially immediately adjacent to the wall of the existing concrete to compact and smooth the subgrade surface substantially up to the edge of the cut out area. Because the sides of the screed head do not have any major projections projecting laterally outwardly therefrom, the ends of the plow or plow wing may engage the subgrade surface substantially adjacent to the side wall of the concrete at least partially surrounding the cut out area. The plow wing on the side of the screed head assembly adjacent to the wall may plow along the edge to move and remove material along the edge of the cut out area. Some minimal manual processing of the surface may be required along the outermost edges of the cut out area to remove any excess material and smooth the areas where the screed head assembly of the present invention may not reach.

[0075] Therefore, the present invention provides a subgrade preparation device or apparatus which prepares or screeds a subgrade to a highly level and smooth surface for receiving a preformed concrete slab thereon. The apparatus of the present invention is operable to lower a screed head assembly down into a cut out area which may be several inches below the level at which the base unit of the apparatus is being supported. The apparatus is then operable to plow and grade the subgrade to a desired level in response to a laser reference plane and is further operable to vibrate and compact the subgrade so that the preformed concrete slab will not encounter settling of the subgrade after it has been placed thereon. The apparatus of the present invention is further capable of preparing the subgrade very close to the edges of the cut out area.

[0076] The apparatus of the present invention thus provides for enhanced smoothing, compacting, and accurate grading of a subgrade surface which is substantially below a level of the concrete surface which supports the subgrade preparation apparatus. Either a flat laser plane reference for flat pre-cast replacement concrete slabs or a pre-programmed three dimensional control system reference for non-flat or warped pre-cast replacement concrete slabs may be used to establish the elevation of the screed head and therefore the accuracy of the finished grade. Because the subgrade preparation apparatus of the present invention is operable to smooth and compact the subgrade surface substantially immediately adjacent to the walls of the cut out area, the present invention provides for subgrade preparation with reduced manual processing of the subgrade surface. Also, the present invention provides a pivotable plow assembly and a pivotable auger assembly to facilitate cleaning and maintenance of the components of the screed head assembly.

[0077] Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the invention, which is intended to be limited only by the scope of the appended claims as interpreted according to the principles of patent law. 

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. A subgrade preparation apparatus for leveling, grading and compacting a subgrade surface for receiving a preformed concrete slab on the subgrade to repair a concrete surface above the subgrade surface, said subgrade preparation apparatus comprising: a base unit positionable on the concrete surface being repaired; an extendable boom extending from said base unit; and a screed head assembly adjustably mounted on said extendable boom, said screed head assembly being vertically adjustable relative to said extendable boom to be lowered into a cut out area of the concrete surface defining the subgrade surface, said screed head assembly including a framework, a plow and at least one of a means for moving material toward at least one side of said screed head assembly and a vibrator mounted to said framework for grading, leveling and/or compacting the subgrade surface, said plow having an outer end, said outer end of said plow defining an outermost portion of said screed head assembly such that said screed head assembly is operable to grade, level, compact and/or smooth the subgrade surface close to the walls of the cut out area.
 2. The subgrade preparation apparatus of claim 1, wherein said plow comprises a main plow and at least one plow wing extending laterally outwardly from said main plow, said outer end of said plow comprising an outer end of said plow wing.
 3. The subgrade preparation apparatus of claim 2, wherein said at least one plow wing is pivotably mounted at said main plow.
 4. The subgrade preparation apparatus of claim 1, wherein said means for moving material toward at least one side of said screed head assembly comprises an auger having a longitudinal rotatable portion rotatably mounted to said screed head assembly.
 5. The subgrade preparation apparatus of claim 4, wherein said auger of said screed head assembly includes at least one outer end of said rotatable portion and a drive motor for rotatably driving said rotatable portion, said drive motor being positioned inward of said at least one outer end of said rotatable portion.
 6. The subgrade preparation apparatus of claim 5, wherein said drive motor is interconnected to said at least one outer end of said rotatable portion via a drive chain, said drive chain being operable to rotate said rotatable portion in response to said drive motor.
 7. The subgrade preparation apparatus of claim 4, wherein said auger is movably mounted to said framework and is movable outward from said framework to provide access to at least one of said plow and said auger of said screed head assembly.
 8. The subgrade preparation apparatus of claim 7, wherein said rotatable portion of said auger is rotatably mounted to a swing arm, which is pivotally mounted to said framework, said swing arm being pivotable to move said auger outward from said framework.
 9. The subgrade preparation apparatus of claim 8, wherein said swing arm is adjustable to adjust a level of said rotatable portion of said auger relative to said screed head assembly.
 10. The subgrade preparation apparatus of claim 8, wherein said plow is pivotally mounted to said framework of said screed head assembly and is pivotable to provide access to at least one of said plow and said auger of said screed head assembly.
 11. The subgrade preparation apparatus of claim 1, wherein said plow is pivotally mounted to said framework of said screed head assembly and is pivotable to provide access to at least one of said plow and said auger of said screed head assembly.
 12. The subgrade preparation apparatus of claim 11, wherein said means for moving material is pivotally mounted to said framework and is pivotable outward from said framework to provide access to said at least one of said plow and said means for moving material of said screed head assembly.
 13. The subgrade preparation apparatus of claim 12, wherein said means for moving material comprises an auger.
 14. The subgrade preparation apparatus of claim 1 including an elevation device which is operable to lower and raise said screed head assembly relative to said extendable boom and said base unit.
 15. The subgrade preparation apparatus of claim 14, wherein said elevation device further includes a tilt limiting device which is operable to limit or substantially preclude excessive vertical movement of one side of said screed head assembly relative to the other side of said screed head assembly.
 16. The subgrade preparation apparatus of claim 14, wherein said elevation device comprises a pair of actuators mounted to said extendable boom and connected to said screed head assembly toward opposite ends of said screed head assembly, said actuators being extendable and retractable to vertically adjust respective sides of said screed head assembly.
 17. The subgrade preparation apparatus of claim 16, wherein said tilt limiting device is operable to deactuate at least one of said actuators in response to a level sensor to limit excessive extension or retraction of said at least one of said actuators relative to the other of said actuators.
 18. The subgrade preparation apparatus of claim 14, wherein said elevation device comprises a pair of hydraulic cylinders having a cylinder and a piston rod extendable and retractable relative to said cylinder.
 19. The subgrade preparation apparatus of claim 18, wherein said cylinders of said elevation device are mounted to said extendable boom and said screed head assembly is mounted to a lower end of said piston rods.
 20. The subgrade preparation apparatus of claim 14, wherein said elevation device is operable in response to a laser reference plane and laser receivers mounted to a portion of said elevation device.
 21. The subgrade preparation apparatus of claim 14, wherein said elevation device is operable in response to a three dimensional profiler system mounted to a portion of said elevation device.
 22. The subgrade preparation apparatus of claim 1 including a second plow mounted to a rearward side of said vibrator.
 23. A method for leveling, grading and/or compacting a subgrade surface for receiving a preformed concrete slab on the subgrade to repair a concrete surface above the subgrade surface, said method comprising: providing a subgrade preparation apparatus comprising a base unit positionable on the concrete surface being repaired and a screed head assembly having a plow which defines at least one end, said screed head assembly having no major projections extending laterally outwardly from said at least one end of said plow; vertically moving said screed head assembly relative to said extendable boom into a cut out area of the concrete surface defining the subgrade; generally horizontally moving said screed head assembly along the subgrade; and grading, leveling and/or compacting the subgrade surface close to the walls of the cut out area with at least one of said plow, a means for moving material to one side of said screed head assembly and a vibrator of said screed head assembly.
 24. The method of claim 23, wherein generally horizontally moving comprises generally horizontally moving said screed head assembly via an extendable boom extending from said base unit.
 25. The method of claim 23 including providing a screed head assembly having a plow, wherein said plow comprises a main plow and at least one plow wing extending laterally outward from said main plow, and outer end of said at least one plow wing defining said at least one end of said plow.
 26. The method of claim 23, wherein said means for moving material to one side of said screed assembly comprises an auger.
 27. The method of claim 26 including rotatably driving said auger of said screed head assembly with a drive motor positioned inward of one of opposite outer ends of said auger.
 28. The method of claim 27, wherein rotatably driving said auger includes rotatably driving said auger with a drive motor and drive chain connected between said drive motor and said one of opposite outer ends of said auger.
 29. The method of claim 26 including pivoting said auger relative to and away from a framework of said screed head assembly to provide access to said at least one of said plow and said auger of said screed head assembly.
 30. The method of claim 23 including pivoting said plow relative to and away from a framework of said screed head assembly to provide access to at least one of said plow and said means for moving material of said screed head assembly.
 31. The method of claim 30 including pivoting said means for moving material relative to and away from said framework to provide access to said at least one of said plow and said means for moving material of said screed head assembly.
 32. The method of claim 23 including limiting excessive vertical movement of one side of said screed head assembly relative to the other side of said screed head assembly.
 33. The method of claim 32, wherein limiting excessive vertical movement includes limiting excessive extension or retraction of at least one of a pair of spaced apart actuators positioned toward opposite sides of said screed head assembly.
 34. The method of claim 33, wherein vertically moving said screed head assembly includes vertically moving said screed head assembly in response to a laser reference plane and laser receivers mounted to a portion of said pair of actuators.
 35. The method of claim 33, wherein vertically moving said screed head assembly includes vertically moving said screed head assembly in response to a three dimensional profiler system mounted to a portion of said pair of actuators.
 36. A subgrade preparation apparatus for leveling, grading and/or compacting a subgrade surface for receiving a preformed concrete slab on the subgrade to repair a concrete surface above the subgrade surface, said subgrade preparation apparatus comprising: a base unit positionable on a concrete surface being repaired; an extendable boom extending from said base unit; and a screed head assembly adjustably mounted on said extendable boom, said screed head assembly being vertically adjustable relative to said extendable boom to be lowered into a cut out area of the concrete surface, the cut out area defining a subgrade surface below the concrete surface, said screed head assembly including a framework and at least one of a plow, a means for moving material toward at least one side of said screed head assembly and a vibrator mounted to said framework for grading, leveling and compacting the subgrade surface; a pair of spaced apart actuators mounted on said extendable boom and connected to said screed head assembly at spaced positions on said screed head assembly, said actuators being operable to extend and retract to vertically move said screed head assembly relative to said extendable boom and said base unit; and a tilt limiting device which is operable to detect a degree of tilt of said screed head assembly and to deactuate at least one of said pair of actuators in response to a threshold degree of tilt of said screed head assembly.
 37. The subgrade preparation apparatus of claim 36, wherein said screed head assembly comprises a plow and at least one of a means for moving material toward at least one side of said screed head assembly and a vibrator.
 38. The subgrade preparation apparatus of claim 37, wherein said plow includes an outer end which defines an outermost portion of said screed head assembly such that said screed head assembly is operable to grade, level, compact and/or smooth the subgrade surface close to at least one wall of the subgrade surface.
 39. The subgrade preparation apparatus of claim 38, wherein said plow comprises a main plow and at least one plow wing extending laterally outwardly from said main plow, said outer end of said plow comprising an outer end of said plow wing.
 40. The subgrade preparation apparatus of claim 36, wherein said screed head assembly defines at least one side surface which has no major projections extending laterally outward therefrom such that said screed head assembly is operable to grade, level, compact and smooth the subgrade surface close to the walls of the cut out area.
 41. The subgrade preparation apparatus of claim 36, wherein said pair of actuators comprises a pair of hydraulic cylinders having a cylinder and a piston rod extendable and retractable relative to said cylinder.
 42. The subgrade preparation apparatus of claim 41, wherein said cylinders are mounted to said extendable boom and said screed head assembly is mounted to a lower end of said piston rods.
 43. The subgrade preparation apparatus of claim 36, wherein said screed head assembly includes at least one plow wing extending laterally outward from said at least one side surface for engaging the subgrade surface along the walls of the cut out area.
 44. The subgrade preparation apparatus of claim 43, wherein said at least one plow wing is pivotably mounted to said at least one side surface of said screed head assembly.
 45. The subgrade preparation apparatus of claim 36, wherein said means for moving material toward at least one side of said screed head assembly comprises an auger having a longitudinal rotatable portion rotatably mounted to said screed head assembly.
 46. The subgrade preparation apparatus of claim 45, wherein said auger of said screed head assembly includes outer ends and a drive motor for driving said auger, said drive motor being positioned inward of one of said outer ends of said auger.
 47. The subgrade preparation apparatus of claim 46, wherein said drive motor is interconnected to said one of said outer ends of said auger via a drive chain, said drive chain being operable to rotate said auger in response to said drive motor.
 48. The subgrade preparation apparatus of claim 45, wherein said auger is pivotally mounted to said framework and is pivotable outward and away from said framework to provide access to at least one of said plow and said auger of said screed head assembly.
 49. The subgrade preparation apparatus of claim 48, wherein said auger is rotatably mounted to a swing arm, which is pivotally mounted to said framework, said swing arm being pivotable to move said auger outward and away from said framework.
 50. The subgrade preparation apparatus of claim 36, wherein said plow is pivotally mounted to said framework of said screed head assembly and is pivotable to provide access to at least one of said plow and said means for moving material of said screed head assembly.
 51. The subgrade preparation apparatus of claim 50, wherein said means for moving material is pivotally mounted to said framework and is pivotable outward and away from said framework to provide access to said at least one of said plow and said means for moving material of said screed head assembly.
 52. The subgrade preparation apparatus of claim 51, wherein said means for moving material comprises an auger.
 53. The subgrade preparation apparatus of claim 36 including a second plow mounted to a rearward side of said vibrator.
 54. A subgrade preparation apparatus for leveling, grading and compacting a subgrade surface for receiving a preformed concrete slab on the subgrade to repair a concrete surface above the subgrade surface, said subgrade preparation apparatus comprising: a base unit positionable on the concrete surface being repaired; an extendable boom extending from said base unit; and a screed head assembly adjustably mounted on said extendable boom, said screed head assembly being vertically adjustable relative to said extendable boom, said screed head assembly including a framework, an auger device for moving material toward at least one side of said screed head assembly and at least one of a plow and a vibrator mounted to said framework for grading, leveling and/or compacting the subgrade surface, said auger device including a rotatable portion rotatably mounted to and extending laterally across said framework and a drive motor for rotatably driving said rotatable portion, said rotatable portion having at least one outer end, said drive motor being positioned at least partially laterally inboard of said at least one outer end of said rotatable portion such that said screed head assembly is operable to grade, level, compact and/or smooth the subgrade surface close to at least one wall at least partially surrounding the subgrade surface.
 55. The subgrade preparation apparatus of claim 54, wherein said drive motor is interconnected to said at least one outer end of said rotatable portion of said auger device via a drive chain, said drive chain being operable to rotate said rotatable portion of said auger device in response to said drive motor.
 56. The subgrade preparation apparatus of claim 54, wherein said auger device is movably mounted to said framework and is movable outward from said framework to provide access to said auger device of said screed head assembly.
 57. The subgrade preparation apparatus of claim 56, wherein said rotatable portion of said auger device is rotatably mounted to a swing arm, said swing arm being pivotally mounted to said framework, said swing arm being pivotable to move said auger device outward from said framework.
 58. The subgrade preparation apparatus of claim 57, wherein said swing arm is adjustable to adjust a level of said rotatable portion relative to said screed head assembly.
 59. The subgrade preparation apparatus of claim 57, wherein said screed head assembly includes a plow, said plow being pivotally mounted to said framework and being pivotable to provide access to at least one of said plow and said auger device.
 60. The subgrade preparation apparatus of claim 54, wherein said screed head assembly includes a plow.
 61. The subgrade preparation apparatus of claim 60, wherein said plow is pivotally mounted to said framework and is pivotable to provide access to at least one of said plow and said auger device.
 62. The subgrade preparation apparatus of claim 60, wherein said plow includes an outer end, said outer end of said plow defining an outermost portion of said screed head assembly such that said screed head assembly is operable to grade, level, compact and/or smooth the subgrade surface close to the at least one wall.
 63. The subgrade preparation apparatus of claim 62, wherein said plow comprises a main plow and at least one plow wing extending laterally outwardly from said main plow, said outer end of said plow comprising an outer end of said plow wing.
 64. The subgrade preparation apparatus of claim 63, wherein said at least one plow wing is pivotably mounted at said main plow.
 65. The subgrade preparation apparatus of claim 54, wherein said screed head assembly is vertically adjustable relative to said extendable boom to be lowerable into a cut out area of the concrete surface defining the subgrade surface, the cut out area defining the at least one wall. 